1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a method of driving a plasma display panel that is adaptive for improving a picture quality.
2. Description of the Related Art
Generally, a plasma display panel (PDP) excites and radiates a phosphorus material using an ultraviolet ray generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development.
FIG. 1 is a perspective view showing a structure of a conventional alternating current (AC) surface-discharge PDP.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes a scan electrode 12Y and a sustain electrode 12Z provided on an upper substrate 10, and an address electrode 20X provided on a lower substrate 18.
On the upper substrate 10 provided with the scan electrode 12Y and the sustain electrode 12Z in parallel, an upper dielectric layer 14 and a protective film 16 are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer 14. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a phosphorous material 26. The address electrode 20X is formed in a direction crossing the scan electrode 12Y and the sustain electrode 12Z. The barrier rib 24 is formed in parallel to the address electrode 20X to thereby prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The phosphorous material 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive gas for a gas discharge is injected into a discharge space defined between the upper and lower substrate 10 and 18 and the barrier rib 24.
Referring to FIG. 2, the conventional AC surface-discharge PDP includes a PDP 30 arranged in a matrix type such that mxn discharge cells are connected to scan electrode lines Y1 to Ym, sustain electrode lines Z1 to Zm and address electrode lines X1 to Xn, a scan driver 32 for driving the scan electrode lines Y1 to Ym, a sustain driver 34 for driving the sustain electrode lines Z1 to Zm, and first and second address drivers 36A and 36B for making a divisional driving of odd-numbered address electrode lines X1, X3, . . . , Xn−3, Xn−1 and even-numbered address electrode lines X2, X4, . . . , Xn−2, Xn. The scan driver 32 sequentially applies a scan pulse and a sustain pulse to the scan electrode lines Y1 to Ym, to thereby sequentially scan discharge cells 1 for each line and sustain a discharge at each of the mxn discharge cells 1. The sustain driver 34 applies a sustain pulse to all the sustain electrode lines Z1 to Zm. The first and second address drivers 36A and 36M apply image data to the address electrode lines X1 to Xn in such a manner to be synchronized with a scan pulse. The first address driver 36A applies image data to the odd-numbered address electrode lines X1, X3, . . . , Xn−3, Xn−1 while applying image data to the even-numbered address electrode lines X2, X4, . . . , Xn−2, Xn.
The AC surface-discharge PDP driven as mentioned above requires a high voltage more than hundreds of volts for an address discharge and a sustain discharge. Accordingly, in order to minimize a driving power required for the address discharge and the sustain discharge, the scan driver 32 and the sustain driver is additionally provided with an energy recovering apparatus 38 as shown in FIG. 3. The energy recovering apparatus 38 recovers a voltage charged in the scan electrode line Y and the sustain electrode line Z and re-uses the recovered voltage as a driving voltage for the next discharge.
Such a conventional driving apparatus 38 includes an inductor L connected between a panel capacitor Cp and a source capacitor Cs, and first and third switches S1 and S3 connected, in parallel, between the source capacitor Cs and the inductor L. A scan/sustain driver 32 is comprised of second and fourth switches S2 and S4 connected, in parallel, between the panel capacitor Cp and the inductor L. The panel capacitor Cp is an equivalent expression of a capacitance formed between the scan electrode line Y and the sustain electrode line Z. The second switch S2 is connected to a sustain voltage source Vsus while the fourth switch S4 is connected to a ground voltage source GND. The source capacitor Cs recovers and charges a voltage charged in the panel capacitor Cp upon sustain discharge and re-supply the charged voltage to the panel capacitor Cp. The source capacitor Cs has a large capacitance value such that it can charge a voltage Vsus/2 equal to a half value of the sustain voltage Vsus. The first to fourth switches S1 to S4 controls a flow of current. The energy recovering apparatus 38 provided at the sustain driver 34 are formed around the panel capacitor Cp symmetrically with the scan driver 32.
FIG. 4 is a timing diagram and a waveform diagram representing on/off timings of the switches shown in FIG. 3 and an output waveform of the panel capacitor.
An operation procedure of the energy recovering apparatus 38 shown in FIG. 3 will be described in conjunction with FIG. 4.
First, it is assumed that a voltage charged between the scan electrode line Y and the sustain electrode line Z, that is, a voltage charged in the panel capacitor Cp prior to the T1 period should be 0 volt, and a voltage Vsus/2 has been charged in the source capacitor Cs. In the T1 period, the first switch S1 is turned on, to thereby form a current path extending from the source capacitor Cs, via the first switch S1 and the inductor L, into the panel capacitor Cp. At this time, the inductor L and the panel capacitor L forms a serial resonance circuit. Since a voltage Vsus/2 has been charged in the source capacitor Cs, a voltage of the panel capacitor Cp rises into a sustain voltage Vsus equal to twice the voltage of the source capacitor Cs with the aid of a current charge/discharge of the inductor L in the serial resonance circuit.
In the T2 period, the second switch S2 is turned on to thereby apply the sustain voltage Vsus to the scan electrode line Y. The sustain voltage Vsus applied to the scan electrode line Y prevents a voltage of the panel capacitor Cp from falling into less than the sustain voltage Vsus to thereby cause a normal sustain discharge. Since a voltage of the panel capacitor Cp has risen into the sustain voltage Vsus in the T1 period, a driving power supplied from the exterior for the purposing of causing the sustain discharge is minimized.
In the T3 period, the first switch S1 is turned off and the panel capacitor Cp keeps the sustain voltage Vsus. In the T4 period, the second switch S2 is turned off while the third switch S3 is turned on. If the third switch S3 is turned on, then a current path extending from the panel capacitor Cp, via the inductor L and the third switch S3, into the source capacitor Cs is formed to thereby recover a voltage charged in the panel capacitor Cp into the source capacitor Cs. While the panel capacitor Cp is discharged, a voltage of the panel capacitor Cp falls. At the same time, a voltage Vsus/2 is charged in the source capacitor Cs. After a voltage Vsus/2 was charged in the source capacitor Cs, the third switch S3 is turned off while the fourth switch S4 is turned on. In the fifth period when the fourth switch S4 is turned on, a current path extending from the panel capacitor Cp into the ground voltage source GND, thereby allowing a voltage of the panel capacitor Cp to falls into 0 volt. In the T6 period, a state in the T5 period is kept for a certain time as it is. An AC driving pulse applied to the scan electrode line Y and the sustain electrode line Z is obtained by periodically repeating an operation procedure in the T1 to T6 periods.
The scan electrode lines Y of the PDP driven in this manner are supplied with a sustain pulse in the sustain period, and are additionally supplied with a reset pulse and a scan pulse in the initialization period and the address period, respectively. Accordingly, the scan driver 32 is provided with a plurality of scan drive integrated circuits and a plurality of high-voltage switches. On the other hand, since the sustain pulse only is supplied, the sustain electrode line Z is directly connected to the sustain driver 34. As a result, a resistance of the current path at the scan driver 32 and the scan electrode line Y becomes larger than that of the current path at the sustain driver 34 and the sustain electrode line Z. Further, the scan driver 32 has a smaller current supply capability than the sustain driver 34.
In spite of such a resistance different of the current path and such a difference in the current supply capability, pulse widths TP1 and TP2 of a first sustain pulse SUS1 and a second sustain pulse SUS2 applied to the scan electrode line Y and the sustain electrode line Z during the sustain period, respectively are equal to each other as shown in FIG. 5. In other words, a rising edge Tr1 of the first sustain pulse SUS1 is identical to a rising edge Tr2 of the second sustain pulse SUS2, and a falling edge Tf1 of the first sustain pulse SUS1 is identical to a falling edge of Tf2 of the second sustain pulse SUS2. Herein, the rising edges Tr1 and Tr2 of the first and second sustain pulses are time intervals going from an operation time of the energy recovering apparatus 38 shown in FIG. 3 until a turning-on time of the second switch S2 while the falling edges Tf1 and Tf2 thereof are time intervals going from an operation time of the energy recovering apparatus 38 into the fourth switch S4.
Accordingly, intensities of sustain discharges caused by the first and second sustain pulses SUS1 and SUS2 applied to the scan electrode line Y and the sustain electrode line Z, respectively are differentiated to raises problems of an irregular discharge and hence a deterioration of picture quality. Particularly, such problems become more serious when a width of each of the first and second sustain pulses SUS1 and SUS2 is approximately 2 μs as a resolution is larger.